1. Field of the Invention
The present invention relates to a printing apparatus, and more particularly, to a cliché unit capable of forming a pattern using a cliché, a printing apparatus, and a printing method using the same.
2. Description of the Related Art
Recently, research into flat panel displays is ongoing. Flat panel displays include a liquid crystal display (LCD), an electro luminescence device (ELD), a plasma display panel (PDP), a vacuum fluorescent display (VFD), and the like.
Among such flat panel displays, the LCD has advantages such as low voltage operation, low power consumption, being lightweight, having a slim profile, and full color realization. Therefore, the LCD is widely used as a display in watches, calculators, computer monitors, television monitors, television sets, and hand-held terminals.
FIG. 1 is a cross-sectional view schematically showing an LCD of the related art.
Referring to FIG. 1, the related art LCD includes: a lower substrate 100 in which liquid crystal cells are arranged in a matrix configuration; an upper substrate 106 facing the lower substrate 100; and a liquid crystal layer 103 interposed between the lower substrate 100 and the upper substrate 106.
The lower substrate 100 includes: a gate electrode 115 formed on an upper surface of a first glass substrate 140 and to which a scanning signal is applied; an active layer 116; a gate insulating layer 117 that electrically isolates the active layer 116 from the gate electrode 115; a source and a drain electrodes 118 and 119 formed on an upper surface of the active layer 116 that applies data signals to the active layer; a passivation layer 120 formed on the gate insulating layer 117 including the source and the drain electrodes 118 and 119; a pixel electrode 121 connected to the drain electrode 119 through a contact hole formed in the passivation layer 120; and a first alignment layer 137 formed on the passivation layer 120 including the pixel electrode 121, for aligning liquid crystal molecules of a liquid crystal layer 103.
The active layer 116 includes a semiconductor layer 116a formed by deposition of amorphous silicon (a—Si) and an ohmic contact layer 116b doped with n+ impurities on both sides of the semiconductor layer 116a. 
The upper substrate 106 includes: a color filter 111 including red, green, and blue sub-color filters on a second glass substrate 110; a black matrix layer 114 formed between the sub-filters to block light; a common electrode 130 made of an indium tin oxide (ITO), transparent conductor, on the color filter 111 and the black matrix layer 114, for applying a common voltage; and a second alignment layer 135 formed on the common electrode 130 to align liquid crystal molecules of the liquid crystal layer 103.
Also, the upper substrate 110 may further include an overcoat layer (not shown) formed on the color filter 111, for reinforcing adhesive force with respect to the common electrode 130 as well as performing planarization of the cooler filter 111.
To manufacture the LCD according to the related art, a pattern or a line may be formed through a photolithography process using an exposure apparatus.
However, such photolithography process requires use of a high price exposure apparatus, which causes problems that not only increase manufacturing costs but also increase manufacturing complexity.
To resolve such problems, a pattern formation method using a Gravure offset printing method has been suggested recently. The Gravure offset printing method is a printing method including placing a resist on a concave plate, scraping residual resist out, and performing printing. The Gravure offset printing method is widely used for a variety of applications such as publications, packaging, cellophane, vinyl, and polyethylene. Recently, an effort to apply the Gravure offset printing method to active LCD display devices or circuit devices has been actively sought for.
The Gravure offset printing method prints a resist on a substrate using a roller. Therefore, a desired pattern may be formed by using a roller one time on an area that corresponds to a desired display device. Accordingly, the Gravure offset printing method may be used to form various patterns on a display device, e.g., a gate line and a data line connected with a thin film transistor, a pixel electrode and a metal pattern for a capacitor, as well as the thin film transistor of the LCD.
FIGS. 2A through 2D show a method for forming a pattern using a Gravure offset printing method.
In FIG. 2A, after a groove 223 corresponding to a pattern is formed on a specific position of a cliché 228, the groove 223 is filled with a resist 225 (or ink). After a resist 225 used to form a pattern is coated on an upper surface of the cliché 228, a doctor blade 224 is moved while it contacts the cliché 228, so that the groove 223 is filled with the resist 225. So while the resist 225 fills the inside of the groove 223 by movement of the doctor blade 224, the resist 225 remaining on a surface of the cliché 228 is removed. Here; the cliché 228 may be made of a material including one of glass, metal, and plastics.
As shown in FIG. 2B, by placing the roller 227 in contact with the surface of the cliché 228 and rotating the roller 227, the resist 225 inside of the grooves 223 of the cliché is transferred to the surface of the roller 227. It is preferable that the width of the cliché 228, the width of a display device to be manufactured, and the circumferential length of the roller 227 are all identical. Therefore, as the roller 227 rotates one time on the surface of the cliché 228, all of the resist 225 inside the grooves 223 of the cliché 228 are transferred to the surface of the roller 227.
As shown in FIG. 2C, as the roller 227 is placed on the surface of an etching-target layer 229 formed on a substrate 230 and rolled, the resist 225 on the roller 227 is printed on the etching-target layer 229. Therefore, because the circumferential length of the roller 227 is the same as the width of the substrate 230, a desired resist 225 pattern may be formed on the entire surface of the substrate 230 by a one-time rotational movement of the roller 227.
Subsequently, as shown in FIG. 2D, the printed resist 225 is heated to dry so that a resist pattern 226 is formed.
As described above, in the Gravure offset printing method, after the resist pattern 226 is formed by using the cliché 228 and the roller 227, the etching-target layer 229 is etched using the resist pattern 226, so that a desired pattern is formed. Therefore, a pattern may be formed in a simple manner as compared with the photolithography process using an exposure apparatus of the related art.
The Gravure offset printing method, however, has a disadvantage. A scratch may be formed on the surface of the cliché 228 due to friction with the doctor blade 224, and as a result, a defect may be easily generated on the surface of the cliché 228. Also, such a scratch or defect is a major factor in generating a bad pattern during the formation of the resist pattern.
FIGS. 3A and 3B show a resist pattern formed on a real cliché and a substrate.
In FIG. 3A, if the cliché rubs against the doctor blade, a scratch may be generated on the surface of the cliché. If a resist pattern is formed on a substrate using a cliché with a scratch, resist in the shape of the scratch on the cliché is transferred onto the substrate.
Thus, if a resist pattern is formed using a cliché with a scratch and the scratch is transferred on the substrate, the substrate cannot be used. When a substrate for a large display is being manufactured, scratches on the cliché greatly increase the manufacturing costs.
The cliché may be manufactured using the following method that includes forming a resist pattern using a photomask on the organic film, after an organic film such as a polymer or a polyimide is deposited on a substrate made of glass, metal, or plastic and performing a dry etching with the resist pattern used for a mask.
To form a desired pattern on a large substrate, a cliché corresponding to such a substrate would also have to be manufactured to have a large size. However, the present technology has a limitation in manufacturing a cliché having a large size, and it is high cost.